Method and system for ultra miniaturized packages for transient voltage suppressors

ABSTRACT

A method of forming a silicon carbide transient voltage suppressor (TVS) assembly and a system for a transient voltage suppressor (TVS) assembly are provided. The transient voltage suppressor (TVS) assembly includes a semiconductor die including a contact surface on a single side of the die, the die further including a substrate comprising a layer of at least one of an electrical insulator material, a semi-insulating material, and a first wide band gap semiconductor having a conductivity of a first polarity, at least a TVS device including a plurality of wide band gap semiconductor layers formed on the substrate; a first electrode coupled in electrical contact with the TVS device and extending to the contact surface, and a second electrode electrically coupled to the substrate extending to the contact surface.

BACKGROUND

The disclosure relates generally to high temperature semiconductordevices, and more specifically, to semiconductor devices for transientvoltage suppression in high temperature environments.

At least some known sensitive electronic equipment use Transient VoltageSuppression (TVS) devices to protect the equipment from lightningstrikes or electromagnetic interference (EMI). High power TVS devicesare typically available only as discrete devices that are electricallycoupled together at the circuit board level to attain the electricalcharacteristics needed in a particular application. Several TVS devicesand/or other components are often connected in parallel and/or series toobtain a required breakdown voltage and current carrying capability.Connecting multiple components together on a circuit board increases thearea of the board considerably, which also increases a weight of forexample, an aircraft and the heat generated by the multiple components.

BRIEF DESCRIPTION

In one embodiment, a transient voltage suppressor (TVS) assemblyincludes a semiconductor die including a contact surface on a singleside of the die, the die further including a substrate comprising alayer of at least one of an electrical insulator material, asemi-insulating material, and a first wide band gap semiconductor havinga conductivity of a first polarity, at least a TVS device including aplurality of wide band gap semiconductor layers formed on the substrate;a first electrode coupled in electrical contact with the TVS device andextending to the contact surface, and a second electrode electricallycoupled to the substrate extending to the contact surface.

In another embodiment, a method of forming a silicon carbide transientvoltage suppressor (TVS) assembly includes providing a silicon carbidesemiconductor transient voltage suppressor (TVS) die that includes afirst side and an opposite contact surface side, coupling a firstelectrode in direct electrical communication with the die and extendingto the contact surface, coupling a second electrode in electricalcommunication with the die and extending to the contact surface, andencapsulating the die, the first electrode, and the second electrode ina flip chip package having the first electrode, and the second electrodeexposed to the contact surface on the same side of the encapsulation.

In yet another embodiment, a high temperature electronic system includesan electronics unit configured for exposure to an environment having atemperature greater than approximately 150.0° C., the remote electronicsunit including a transient voltage suppressor (TVS) assembly coupled inoperative relationship with at least some electronic components of theelectronics unit, the TVS assembly including at least one TVS deviceincluding at least one of a punch-through wide band-gap semiconductorTVS die and an avalanche breakdown wide band-gap semiconductor TVS dieencapsulated in a flip-chip package at least partially surrounding thedie, and coupled to electrodes exposed to a single side of theencapsulation.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of the presenttechnique will become better understood when the following detaileddescription is read with reference to the accompanying drawings in whichlike characters represent like parts throughout the drawings, wherein:

FIG. 1 is a side elevation view of a transient voltage suppression (TVS)assembly in accordance with an exemplary embodiment of the presentsystem;

FIG. 2 is a schematic diagram of the TVS assembly shown in FIG. 1;

FIG. 3 is a side elevation view of a TVS assembly in accordance withanother embodiment of the present system;

FIG. 4 is a side elevation view of a TVS assembly in accordance withstill another exemplary embodiment of the present invention;

FIG. 5 is a side elevation view of a TVS assembly in accordance with yetanother exemplary embodiment of the present invention;

FIG. 6 is a side elevation view of a TVS assembly in accordance withanother exemplary embodiment of the present invention;

FIG. 7A is a cutaway plan view of a TVS package in accordance with anexemplary embodiment of the present invention;

FIG. 7B is a side elevation view of the TVS package shown in FIG. 7A;

FIG. 8A is a cutaway plan view of a TVS die according to the presenttechnique;

FIG. 8B is a side elevation view of the TVS die shown in FIG. 8A;

FIG. 9A is a cutaway plan view of a TVS package according to the presenttechnique;

FIG. 9B is a side elevation view of the TVS package shown in FIG. 9A;

FIG. 10A is a cutaway plan view of a TVS die according to the presenttechnique; and

FIG. 10B is a side elevation view of the TVS die shown in FIG. 10A.

DETAILED DESCRIPTION

The following detailed description illustrates embodiments of the systemby way of example and not by way of limitation. It is contemplated thatthe systems and methods have general application to electronic componentmanufacturing and packaging in power electronics, signal electronics,and electromagnetic interference (EMI) protection in industrial,commercial, and residential applications.

As used herein, an element or step recited in the singular and precededwith the word “a” or “an” should be understood as not excluding pluralelements or steps, unless such exclusion is explicitly recited.Furthermore, references to “one embodiment” of the present invention arenot intended to be interpreted as excluding the existence of additionalembodiments that also incorporate the recited features.

Embodiments of the present disclosure demonstrate a semiconductor basedTVS device that includes flip-chip packaging methods to reduce theoverall area of the package. In various embodiments, a plurality of highpower TVS devices are combined in the same package to provide protectionfor multiple I/O lines from a single device. The TVS device may includea PN junction diode connected in series with the TVS device in thesingle package if a very low capacitance, for example, approximately 10picoFarads (pF) to approximately 20 pF is required, for example, if theTVS is used protect communication lines. Coupling a relatively highcapacitance TVS device to a load may tend to adversely load thedownstream electronics. As described herein, the PN junction diode isalso combined electrically with the TVS device in the same die, therebyreducing the overall area of the TVS assembly.

Currently, known TVS devices are used extensively in several areas inelectrical systems, for example, the electrical systems of an aircraft.For example, a FADEC has approximately 200 TVS parts in it. Thesedevices occupy valuable board area, especially if multiple devices areconnected in series in order to achieve a predetermined breakdownvoltage/power rating combination or if multiple devices are needed toconnect a plurality of input/output (I/Os) devices in close proximity.Embodiments of the present disclosure describe methods and apparatusconfigured to reduce the size of the TVS device by (a) using a wideband-gap semiconductor-based device rather than silicon-basedsemiconductor devices, (b) combining a TVS device and a diode on thesame die, (c) using flip-chip packaging methods, and/or (d) combiningseveral TVS parts inside the same package.

FIG. 1 is a side elevation view of a transient voltage suppression (TVS)assembly 100 in accordance with an exemplary embodiment of the presentsystem. In the exemplary embodiment, TVS assembly 100 includes a TVSdevice 102 and a PN junction 104 electrically coupled in series througha semiconductor layer 106 comprising a first polarity, for example, anN+ polarity based on the doping implemented in the fabrication ofsemiconductor layer 106. Semiconductor layer is grown on or coupled to asubstrate 108. In various embodiments, substrate 108 may be fabricatedfrom an electrical insulator material, a semi-insulating material, or afirst wide band gap semiconductor having a conductivity of the firstpolarity. In one embodiment, substrate 108 is formed of an insulatingmaterial, for example, but not limited to, Silicon Dioxide (SiO₂),Sapphire, and quartz or a semi-insulating material such as, but notlimited to, un-doped Silicon Carbide.

TVS device 102 includes a mesa structure that is formed on semiconductorlayer 106. An epitaxially grown P− layer 110 is coupled in electricalcontact with semiconductor layer 106. An epitaxially grown N+ layer 112is coupled in electrical contact with P− layer 110. In the exemplaryembodiment, P− layer 110 is relatively lightly doped relative to the N+layers 106 and 112. A uniform doping concentration of semiconductorlayer 106 and layers 110 and 112 improves a uniformity of the electricfield distribution in the depletion region of layer 110, therebyimproving the breakdown voltage characteristic. Moreover, the mesastructure has a beveled sidewall angled approximately five degrees toapproximately 90 degrees with respect to an interface between adjacentcontacting layers to reduce the maximum electric field profile at asurface of the die. A first electrical contact 114 is coupled inelectrical contact with layer 112 and extends to a contact surface 115of TVS assembly 100.

PN junction 104 is formed similarly as TVS device 102. An epitaxiallygrown P− layer 118 is coupled in electrical contact with layer 106. Asecond electrical contact 120 is coupled in electrical contact withlayer 118 and extends to contact surface 115. Electrical contacts 114and 120 may be formed by sputtering, vapor deposition, evaporation, orother method for adhering a metal contact surface to semiconductorsurfaces of layers 112 and 118. In various embodiments, electricalcontacts 114 and 120 include sublayers of different materials. Forexample, contacts 114 and 120 may include a first sublayer 122comprising, for example, nickel (Ni), which possesses good adherencecharacteristics with respect to the semiconductor material of layer 112and 118. A second sublayer 124 comprising for example, tungsten (W) isdeposited onto Ni sublayer 122 and a third sublayer comprising, forexample, gold (Au) is deposited onto W sublayer 124. W and Au are usedto provide lower resistivity for electrical contacts 114 and 120.Although, described herein as comprising sublayers of Ni, W, and Au, itshould be recognized that electrical contacts 114 and 120 may comprisemore or less that three sublayers comprising the same or differentmaterials than Ni, W, and Au, or alloys thereof.

In the exemplary embodiment, TVS assembly 100 is formed in a “flip chip”configuration. Accordingly, electrical contacts 114 and 120 are orientedon the same side of TVS assembly 100. Moreover, TVS device 102 operatesusing “punch-through,” or also known as, “reach-through” physics suchthat as the voltage across TVS device 102 is increased, a depletionregion extends all across P− layer 110 and touches N+ layers 106 and112. This leads to a condition known as “punch-through” and largeamounts of current are able to flow through TVS device 102. TVS device102 is able to maintain this condition with minimal change in thevoltage across it.

In various embodiments, TVS device 102 is sized and formed to ensure amaximum electric field internal to the semiconductor material of TVSdevice 102 is maintained less than two megavolts per centimeter.Additionally, TVS device 102 is configured to maintain an increase inblocking voltage of less than 5% for current in a range of less thanapproximately 1.0 nanoamp to approximately 1.0 milliamp. As used herein,blocking voltage refers to the highest voltage at which TVS device 102does not conduct or is still in an “off” state. Moreover, TVS device 102is configured to maintain an electrical leakage current of less thanapproximately 1.0 microamp up to approximately the punch-through voltageof TVS device 102 at room temperature and less than 1.0 microamp up toapproximately the punch-through voltage at operating temperatures of upto 225° Celsius.

In various embodiments, TVS device 102 is configured to exhibit punchthrough characteristics between approximately 5.0 volts to approximately75.0 volts. In various other embodiments, TVS device 102 is configuredto exhibit punch through characteristics between approximately 75.0volts to approximately 200.0 volts. In still other embodiments, TVSdevice 102 is configured to exhibit punch through characteristicsgreater than approximately 200 volts.

Although the semiconductor material used to form TVS device 102 and PNjunction 104 is described herein as being silicon carbide, it should beunderstood that the semiconductor material may include other wideband-gap semiconductors capable of performing the functions describedherein and in the environments described herein.

FIG. 2 is a schematic diagram of TVS assembly 100 (shown in FIG. 1). TVSassembly 100 includes TVS device 102 electrically coupled in series withPN junction 104 through substrate 106.

FIG. 3 is a side elevation view of a TVS assembly 300 in accordance withan embodiment of the present system. In the exemplary embodiment, TVSassembly 100 includes a TVS device 302 and a PN junction 304electrically coupled in series through a semiconductor substrate 306comprising a first polarity, for example, an N+ polarity based on thedoping implemented in the fabrication of substrate 306. In the exemplaryembodiment, PN junction 304 facilitates reducing an impedance,specifically a capacitance of TVS assembly 300 to reduce electricalloading on downstream components.

TVS assembly 300 operates using a different electrical principle thanTVS assembly 100 (shown in FIG. 1). Whereas TVS assembly 100 operatesusing “punch through” physics, TVS assembly 300 uses “avalanchebreakdown”, which is the result of carrier “impact ionization.” Impactionization is a process that occurs in a space charge region ordepletion region of TVS device 302 under a sufficiently high electricfield which is the result of the voltage difference across TVS device302. At that high field the net electron/hole generation rate due toimpact ionization exceeds a critical value, enabling the current to riseindefinitely due to a positive feedback mechanism.

TVS device 302 includes a mesa structure that is formed on substrate 306of for example, silicon carbide or other wide band-gap semiconductormaterial having an N+ type conductivity. In the exemplary embodiment, anN+ type conductivity layer 308 is epitaxially grown on substrate 306. Afirst epitaxially grown P− layer 310 is coupled in electrical contactwith layer 308. An epitaxially grown P+ layer 312 is coupled inelectrical contact with P− layer 310. A second epitaxially grown P−layer 314 is coupled in electrical contact with layer 312. A second N+type conductivity layer 316 is epitaxially grown on P− layer 314. Afirst electrical contact 318 is coupled in electrical contact with layer316 and extends to a contact surface 319.

PN junction 304 is formed similarly as TVS device 302. An N+ typeconductivity layer 320 is epitaxially grown on substrate 306. Anepitaxially grown P− layer 322 is coupled in electrical contact withlayer 320. An epitaxially grown P+ layer 324 is coupled in electricalcontact with P− layer 322. A second electrical contact 326 is coupled inelectrical contact with layer 324 and extends to contact surface 319.Similar to TVS assembly 100, electrical contacts 318 and 326 may beformed by sputtering, vapor deposition, evaporation, or other method foradhering a metal contact surface to semiconductor surfaces of layers 316and 324. In various embodiments, electrical contacts 318 and 326 areformed identically to electrical contacts 114 and 120 (shown in FIG. 1).

Although the semiconductor material used to form TVS device 302 and PNjunction 304 is described herein as being silicon carbide, it should beunderstood that the semiconductor material may include other wideband-gap semiconductors capable of performing the functions describedherein and in the environments described herein.

FIG. 4 is a side elevation view of a TVS assembly 400 in accordance withan exemplary embodiment of the present invention. In the exemplaryembodiment, TVS assembly 400 includes only a punch-through based TVSdevice 402 in a “flip-chip” configuration wherein each of for example,two electrical contacts 404 and 406 to circuitry offboard TVS assembly400 extend to a contact surface 408. TVS assembly 400 is substantiallysimilar to TVS assembly 100 (shown in FIG. 1) without a PN junction.

FIG. 5 is a side elevation view of a TVS assembly 500 in accordance withan exemplary embodiment of the present invention. In the exemplaryembodiment, TVS assembly 500 includes only an avalanche-breakdown basedTVS device 502 in a “flip-chip” configuration wherein each of forexample, two electrical contacts 504 and 506 to circuitry offboard TVSassembly 500 extend to a contact surface 508. TVS assembly 500 issubstantially similar to TVS assembly 300 (shown in FIG. 3) without a PNjunction.

FIG. 6 is a side elevation view of a TVS assembly 600 in accordance withan exemplary embodiment of the present invention. In the exemplaryembodiment, TVS assembly 600 may include a punch-through oravalanche-breakdown based TVS device 602 and may or may not include acapacitance-reducing PN junction formed in electrical series with TVSdevice 602. TVS assembly 600 is shown flipped onto a printed circuitboard 604 having conductive traces 606 and 607 routed alongpredetermined paths to carry current between various components mountedon printed circuit board 604. In the exemplary embodiment, solder 608 isused to electrically connect a first electrical contact 610 to trace 606and to electrically connect a second electrical contact 612 to trace607.

FIG. 7A is a cutaway plan view of a TVS package 700 in accordance withan exemplary embodiment of the present invention. FIG. 7B is a sideelevation view of TVS package 700. In the exemplary embodiment, TVSpackage 700 includes a plurality of individual TVS devices 702fabricated as independent devices on the same semiconductor die 703. Inthe exemplary embodiment, each semiconductor die 703 is electricallycoupled to traces 704 that are routed among various components on acircuit board (not shown in FIG. 7A or 7B). Also in the exemplaryembodiment, one electrical terminal 706 of each semiconductor die 703 iscoupled to a common trace 708, such as, an electrical ground. In variousembodiments, electrical terminals 706 of each semiconductor die 703 arecoupled to other than common trace 708. TVS package 700 may beencapsulated or over-molded using, for example, but not limited to aplastic. Electrical terminals 706 are electrically coupled to traces 704and 708 using, for example, but not limited to, solder, transient liquidphase (TLP) bonding, and thermocompression bonding. As used herein,transient liquid phase bonding refers to a joining process for bondingmetallic systems. TLP produces joints with a uniform compositionprofile, tolerant of surface oxides and geometrical defects, and aremelt temperature higher than the bonding temperature. For example, inthe exemplary embodiment, the interlayer and parent metal compositionsare selected such that the TLP bond has a bonding temperature ofapproximately 280° C. and a remelt temperature of approximately 600° C.In various embodiments, the TLP bond may include gold rich, gold, silveror nickel tin, indium, or combinations thereof. Additionally, other TLPinterlayers and parent metals are contemplated.

FIG. 8A is a cutaway plan view of TVS die 703 in accordance with anotherembodiment of the present invention. FIG. 8B is a side elevation view ofTVS die 703. In the exemplary embodiment, TVS die 703 includes aplurality of individual TVS devices 702 fabricated as independentsemiconductor circuits. The individual TVS circuits may be coupledtogether in series, parallel, or a combination thereof. In the exemplaryembodiment, each semiconductor die 703 is electrically coupled to traces804 that are routed among various components on a circuit board (notshown in FIG. 8A or 8B). Also in the exemplary embodiment, anotherelectrical terminal 806 of each semiconductor die 703 is coupled to acommon trace 808, such as, an electrical ground. In various embodiments,electrical terminals 806 of each semiconductor die 703 are coupled toother than common trace 808.

FIG. 9A is a cutaway plan view of a TVS package 900 in accordance withan exemplary embodiment of the present invention. FIG. 9B is a sideelevation view of TVS package 900. In the exemplary embodiment, TVSpackage 900 includes a plurality of individual TVS devices 702fabricated as independent devices on the same semiconductor die 703. Inthe exemplary embodiment, each semiconductor die 703 is electricallycoupled to traces 704 and 908 that are routed among various componentson a circuit board (not shown in FIG. 9A or 9B). In various embodiments,trace 704 or trace 908 is coupled to, for example, an electrical ground.TVS package 700 may be encapsulated or over-molded using, for example,but not limited to a plastic. Electrical terminals 906 are electricallycoupled to traces 704 and 908 using, for example, but not limited to,solder, transient liquid phase (TLP) bonding, and thermocompressionbonding as described above.

FIG. 10A is a cutaway plan view of a TVS die 1003 in accordance withanother embodiment of the present invention. FIG. 10B is a sideelevation view of TVS die 1003. In the exemplary embodiment, TVS die1003 includes a plurality of individual TVS devices 702 fabricated asindependent semiconductor circuits. The individual TVS circuits may becoupled together in series, parallel, or a combination thereof. In theexemplary embodiment, each semiconductor die 1003 is electricallycoupled to traces 804 and 1008 that are routed among various componentson a circuit board (not shown in FIG. 10A or 10B). In variousembodiments, trace 804 or trace 1008 is coupled to, for example, anelectrical ground.

In various embodiments, the TVS devices are illustrated as mesastructures, however the TVS devices can also be formed in frusto-conicalstructures, cylindrical structures, or combinations thereof, forexample, a frusto-conical portion and cylindrical portion formed inseries, or two frusto-conical portion formed in series.

Where a semiconductor is referred to as having one type of polaritylayer coupled to a different polarity layer, it should be understoodthat the device formed by the semiconductor materials is capable of alsooperating when the polarities of the layers is reversed. Examples ofonly one configuration are given for simplicity in the explanation.

The above-described embodiments of a method and system of transientvoltage suppression provides a cost-effective and reliable means forreducing and/or eliminating voltage spikes induced into electricalsystems such as from EMI and/or lightning strikes. More specifically,the methods and systems described herein facilitate high density wideband-gap TVS structures that are physically smaller and moreenvironmentally robust than typical silicon-based semiconductor devices.In addition, the TVS devices described herein reduce the circuit boardarea required to site the devices, which directly aids in increasing thedensity of the rest of the system electronics. Moreover, by using alesser number of TVS devices, the overall system weight is reduced.Because of the use of wide-band gap semiconductor materials, such as,but not limited to, silicon carbide, the TVS devices can be used in ahigh temperature environment, for example, environments greater than150.0° Celsius. By combining several TVS devices into one die and byreducing the area of the die itself through the usage of SiC or otherwide band-gap semiconductors, the cost of TVS assemblies can be reduced.In addition, the above-described methods and systems facilitateoperating electronic components in high density housings withoutadditional cooling support. As a result, the methods and systemsdescribed herein facilitate operating vehicles, such as aircraft in acost-effective and reliable manner.

This written description uses examples to disclose the invention,including the best mode, and also to enable any person skilled in theart to practice the invention, including making and using any devices orsystems and performing any incorporated methods. The patentable scope ofthe invention is defined by the claims, and may include other examplesthat occur to those skilled in the art. Such other examples are intendedto be within the scope of the claims if they have structural elementsthat do not differ from the literal language of the claims, or if theyinclude equivalent structural elements with insubstantial differencesfrom the literal languages of the claims.

The invention claimed is:
 1. A transient voltage suppressor (TVS)assembly having a semiconductor die comprising a contact surface on asingle side of said die, said die further comprising: a substratecomprising a layer of at least one of an electrical insulator material,a semi-insulating material, and a first wide band gap semiconductorhaving a conductivity of a first polarity; at least a TVS devicecomprising a plurality of wide band gap semiconductor layers formed onsaid substrate; a first electrode coupled in electrical contact withsaid TVS device and extending to said contact surface; a secondelectrode electrically coupled to said substrate extending to saidcontact surface, further comprising a beveled sidewall forming an angleof approximately five degrees to approximately ninety degrees withrespect to an interface between adjacent contacting layers; a secondlayer of the first wide band gap semiconductor or a second wide band gapsemiconductor having a conductivity of a second polarity coupled inelectrical contact with said substrate, the second polarity beingdifferent than the first polarity; and a third layer of the first, thesecond, or a third wide band gap semiconductor having a conductivity ofthe first polarity coupled in electrical contact with said second layer,said second layer having a conductivity of the second polarity islightly doped relative to the layers having a conductivity of the firstpolarity.
 2. A TVS assembly in according with claim 1, furthercomprising a PN junction formed in series with said TVS device.
 3. A TVSassembly in according with claim 1, wherein said TVS device operates ina punch-though mode.
 4. A TVS assembly in according with claim 1,wherein said layer having a conductivity of a first polarity comprisesan n+ type conductivity layer and said layer having a conductivity of asecond polarity comprises a p− type conductivity layer.
 5. A TVSassembly in according with claim 1, wherein said layer having aconductivity of a first polarity comprises a p+ type conductivity layerand said having a conductivity of a second polarity comprises an n− typeconductivity layer.
 6. A TVS assembly in according with claim 1, whereinsaid TVS device operates in an avalanche breakdown mode.
 7. A TVSassembly in according with claim 1, wherein said TVS device comprises: asecond layer of the first wide band gap semiconductor or a second wideband gap semiconductor having a conductivity of a second polaritycoupled in electrical contact with said substrate, the second polaritybeing different than the first polarity; a third layer of the first, thesecond, or a third wide band gap semiconductor having a conductivity ofthe second polarity coupled in electrical contact with said secondlayer, said third layer being lightly doped relative to the layershaving a conductivity of the first polarity; a fourth layer of thefirst, the second, or the third wide band gap semiconductor having aconductivity of the second polarity coupled in electrical contact withsaid third layer; and a fifth layer of the first, the second, or thethird wide band gap semiconductor having a conductivity of the firstpolarity coupled in electrical contact with said fourth layer, when avoltage greater than a predetermined magnitude is applied across thefirst and second electrodes, free electrons moving through the TVSdevice knock other electrons free, creating more free-electron-holepairs increasing the current flow through the TVS assembly to arelatively large amount of current flow.
 8. A TVS assembly in accordingwith claim 1, wherein said layer having a conductivity of a firstpolarity comprises an n+ type conductivity layer and said layer having aconductivity of a second polarity comprises a p− type conductivitylayer.
 9. A TVS assembly in according with claim 1, wherein said layerhaving a conductivity of a first polarity comprises a p+ typeconductivity layer and said having a conductivity of a second polaritycomprises an n− type conductivity layer.
 10. A TVS assembly in accordingwith claim 1, wherein said layers of semiconductor of said TVS deviceare formed by at least one of epitaxial growth, diffusion, and ionimplantation.
 11. A TVS assembly in according with claim 1, wherein saidsubstrate and said layers comprise at least one of silicon carbide(SiC), gallium nitride (GaN), diamond, aluminum nitride (AlN), boronnitride (BN), and combinations thereof.
 12. A TVS assembly in accordingwith claim 1, wherein said substrate is formed by diffusion of a dopantinto a wide band gap semiconductor layer.
 13. A TVS assembly inaccording with claim 1, wherein at least one of said TVS device andanother semiconductor device are formed in a single frusto-conicalcross-section, a multiple frusto-conical cross-section, cylindricalcross-section, or combinations thereof.